A solar cell and a power generation system are a technology for directly converting solar energy into electrical energy and receive sunlight and then immediately generate electricity by using the solar cell made up of a semiconductor, dye, polymer, etc. Compared with this, a solar power generation is provided which absorbs the radiant energy of the sun and converts into thermal energy.
Photovoltaic (PV) power generation changes directly unlimited, non-polluting solar energy into electrical energy, and is comprised of a solar cell (module), PCS, power storage device, etc. The most common silicon solar cell is manufactured by joining a p-type semiconductor and an n-type semiconductor (p-n junction) and by coating a transparent conductive film and a metal electrode on both ends of the p-n junction semiconductor. When sunlight is incident on and absorbed into the inside of the semiconductor, electrons and electron holes are generated and are pulled into an electric field by p-n junction. Then, the electrons move to the n-side and the electron holes move to the p-side, and thus, current flows through an external circuit. A photovoltaic system is comprised of a part (module) which receives light and converts the light into electricity and a part (PCS) which converts the generated electricity into alternating current to meet the demand and connects the alternating current to a system.
The core part of the parts constituting the photovoltaic System is a solar cell. The solar cell performs a basic semiconductor device technology, that is, a function of converting sunlight into electrical energy. The solar cell has the same basic structure and the same material characteristics as those of an information display device like laser, a light emitting diode (LED), etc., which convert electricity into light, and just has a reverse operation direction to that of the information display device.
The minimum unit of the solar cell is referred to as a cell. Generally, since one cell outputs a very low voltage, i.e., about 0.5 V, it is necessary to obtain a voltage and output in a practical range in accordance with a range of use by a plurality of solar cells in series or in parallel. Here, for this, a power generator manufactured by being packaged in one piece is referred to as a photovoltaic (PV) module.
The photovoltaic module is manufactured in the form of a panel by using glass, a buffer material, a surface material, etc., in order to protect the solar cell from external environments. The photovoltaic module includes an external terminal which has durability and weather resistance and is used to extract the power. A power generator configured in conformity with a use range by electrically connecting a plurality of photovoltaic modules in series or in parallel through use of a rack and a support in consideration of an installation condition such as an inclination angle, azimuth angle, etc., such that more sunlight can be incident on the plurality of photovoltaic modules is referred to as a photovoltaic (PV) array.
A power conditioning system (PCS) for photovoltaic power generation refers to an inverter which converts direct current (DC) power generated from the photovoltaic array into alternating current (AC) power. The inverter converts direct current (DC) power generated from the photovoltaic array into alternating current (AC) power having a voltage and frequency like a commercial system. Therefore, the PCS is referred to as the inverter. The PCS is composed of an inverter, a power controller, and a protector. The PCS is the largest part among the peripheral devices other than the main body of the solar cell.
The thin film solar cell requires much less amount of a raw material used than that of a crystalline silicon solar cell, has a larger area and can be mass-produced. Therefore, the manufacturing cost of the thin film solar cell can be reduced. Also, the thin film solar cell has a light absorption layer of which the thickness is several μm, and thus, consumes a very small amount of the raw material. The fifth generation class large area module can be manufactured. The solar cell and the module are manufactured together, so that a simple value chain is obtained. Also, as shown in FIG. 1, a thin film solar cell (module) using a silicon thin film and a compound thin film like CI(G)S and CdTe, etc., is being commercialized.
ACTS thin film or CIGS thin film is a kind of a compound semiconductor and has the highest conversion efficiency (20.3%) among the thin film solar cells manufactured experimentally. Particularly, the CIS thin film or CIGS thin film can be manufactured to have a thickness 10 microns or less and is stable even when used for a long time, so that it is now increasingly taking the place of silicon.
In particular, the CIS thin film is a direct transition semiconductor and can be thinner. The CIS thin film has a band gap of 1.04 eV and is suitable for optical conversion. The CIS thin film has a large light absorption coefficient among known solar cell materials. The CIGS thin film has been developed by replacing a portion of In with Ga or replacing S with Se in order to improve a low open circuit voltage of the CIS thin film.
A CIGS-based solar cell is manufactured by using a thin film having a thickness of several microns. The manufacturing method thereof includes a method using deposition in vacuum and a method applying a precursor material and performing a heat treatment process in non-vacuum. The method using deposition in vacuum is capable of manufacturing an absorption layer with high efficiency. However, when a large area absorption layer is manufactured, it has a low uniformity, has to use a high-priced equipment, and has a high manufacturing cost due to the loss of 20 to 50% of the material to be used. Meanwhile, the method applying a precursor material and performing a high temperature heat treatment process is able to reduce the process cost and uniformly manufacture the large area, however, has a relatively low efficiency of the absorption layer.
The CIGS thin film manufactured by applying the precursor material in non-vacuum has a lot of pores and is not dense. Therefore, a selenization heat treatment process is performed. Since a conventional selenization heat treatment process uses toxic hydrogen selenide (H2Se), a very high cost of equipment is required so as to provide safety equipment and a long term heat treatment process is required, so that the manufacturing cost of the CIGS thin film is high. Also, a melting point of the CIGS thin film is very high over 1,000° C. Therefore, in even CIGS compound nano particles having a size of several tens of nanometers, it is not easy to obtain grain growth and densification due to a post heat treatment.
Due to the above problem, there is a requirement for the material of the light absorption layer other than the CIGS.
Japanese Patent Application Laid-open No. 2009-004773 discloses a solid photovoltaic device including a form of MxSbySz (M=Ag or Cu). Japanese Patent Application Laid-open No. 2009-004773 discloses the solid photovoltaic device which has an interpenetration structure in which three all solid inorganic components (two transparent n-type semiconductors and transparent p-type semiconductors, and one absorber) which maintain a sufficient photovoltaic performance at a low cost is used as a base. The solid photovoltaic device includes three inorganic solid materials including a composition of at least one absorber compound which exists as a continuous layer between a transparent n-type semiconductor compound and a transparent p-type semiconductor compound and does not contact the transparent n-type semiconductor compound and the transparent p-type semiconductor compound. One side of the transparent n-type semiconductor compound or the transparent p-type semiconductor compound exists as a porous substrate having a plurality of pores. The inner surfaces of the plurality of pores are wholly covered with the thin and continuous absorption layer of the absorber compound, so that the plurality of pores are filled at a volume ratio greater than at least 10% thereof with a cover layer made of the one side of the transparent p-type semiconductor compound or the transparent n-type semiconductor compound. The absorption layer includes at least one compound based on antimony and silver sulfide or one compound based on antimony and copper sulfide. However, the solid photovoltaic device disclosed in Japanese Patent Application Laid-open No. 2009-004773 has a fuel sensitizing type structure and is different from a below-described thin films solar cell according to an embodiment of the present invention.